I have the following JSON object, from which I need to retrieve values of certain keys. For example, in outer JSON object, I need only "timestamp" and "type", next from a nested "meta" object I need only "version", and from nested "payload" I want fields "reason", "type" and "condition" from its nested object "data"
{
"timestamp": "1568961295627",
"type": "test",
"namespace": "internal",
"meta": {
"version": "2.0-test",
"id": "123"
},
"payload": {
"data": {
"reason": "user_request",
"type": "asd",
"condition": "bad"
},
"contentType": "application/json"
}
}
I wrote a function to retrieve such data:
void log_values(json_t *data) {
json_t *obj = NULL;
json_t *nested = NULL;
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(data, "timestamp")));
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(data, "type")));
obj = json_object_get(data, "meta");
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(obj, "version")));
obj = json_object_get(data, "payload");
nested = json_object_get(obj, "data");
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(nested, "reson")));
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(nested, "type")));
syslog(LOG_INFO, "%s: ", json_string_value(json_object_get(nested, "condition")));
}
However, the code looks repetitive and I'm wondering if there is any way to generalize it? The first thing which came to mind is to create a jagged array of pointers to keys needed for each stage, and then walk through the array and retrieve only certain keys on certain nesting level, for example:
char *nested0 = {"timestamp", "type"};
char *nested1 = {"anomaly", "version"};
char *nested2 = {"reason", "type", "condition"};
char *(*keys[])[] = { &nested0, &nested1, &nested2 }
But, this solution does not solve problem regarding where to store key names, which point to nested JSONs (e.g "meta, payload, data").
So, the question is: How to generalize the aforementioned code and what data structure should I use to store names of keys holding a json object and keys for which I need to get values.
Take a look at jsmn, it should fit your needs : https://github.com/zserge/jsmn
exemple of what you could do with jsmn :